Hose clamps of this type (German Patent No. 30 41 106, German Patent No. 36 33 486) are intended and suited particularly for hose systems having average internal pressures, such as motor vehicle engine coolant systems, where internal pressures during operation of a maximum of 2 bar can be expected. Typically, such hose systems are tested at up to 3 bar. The pressuretight seat of a hose end on an attachment fitting of such a hose system is assured on the one hand by the intrinsic elasticity of the hose end itself, which is usually a rubber hose or rubber-plastic hose with reinforcing fabric and so forth, and on the other hand by the spring force of the hose clamp referred to above. That is, the known hose clamp is not tightened by a separate tightening element, such as a tightening screw, in order to bring about the pressuretight seat of a hose end on a connection fitting; instead, the spring force of the correspondingly severely prestressed hose clamp itself assures the pressuretight seat. The force that must be brought to bear by a tool on the tightening ends of the hose clamp in order to spread a hose clamp apart to a considerably greater diameter, typically a maximally limited diameter, counter to its own spring force is correspondingly great. This diameter must suffice to move the hose clamp easily, up to some intended position, over the hose end is seated on the connection fitting.
The known hose clamp referred to above is slipped onto the connection fitting or onto the hose end in the spread-apart state. To this end, the two tightening ends are already interlocked with one another in the spread-apart state of the clamp body at the factory. On site, before the hose clamp is installed in a hose system, the tightening ends need merely be unlocked from one another, as soon as the hose clamp is located at the intended position. As a result, a special tightening tool for manipulation on site is not necessary. For unlocking, the shackle need merely be pulled radially outward, so that it slides downward from the end, embodied as a detent protrusion, of the other tightening end. Because only a substantially radial displacement of the detent protrusion relative to the detent recess in the shackle is necessary for unlocking here, the unlocking can be performed with a relatively slight exertion of force, since the effective spring force of the hose clamp in the spread-apart state is directed substantially at a tangent.
Functionally, the known hose clamp is particularly suitable and in particular is easily unlocked. This hose clamp is also favorable from a manufacturing standpoint as well as in terms of cost, because it is made completely in one piece. However, it has been found in practice that excessively often, the tightening ends still come unlocked unintentionally, in particular before the clamp has been installed on the connection fitting or on the hose end.